More and more products are desirably including radio frequency (RF) circuits associated therewith. An important element of such RF circuits is an RF antenna, which must have a configuration where two substantial bodies of conductive material are properly spaced from each other so as to define two antenna portions which are bridged by a circuit chip comprising an RF transponder. The antennas are typically produced by utilizing conductive ink (such as shown in co-pending application Ser. No. 09/408,519 filed Sep. 29, 1999, the disclosure of which is hereby incorporated by reference herein) and in which the conductive ink can be printed as numbers or letters or in some other configuration that is aesthetic, or, such as shown in U.S. Pat. Nos. 5,223,801 and 5,786,626 (the disclosures of which are hereby incorporated by reference herein). The antenna may be in the form of etched or stamped conductive foil. While products made from such structure function properly, the conductive ink does not provide a high grade antenna since it cannot be as thick or as conductive, in general, as can a conductive foil. On the other hand the conventional etching or stamping techniques for applying foil do not lend themselves to high speed production, and do not allow the variability in the configuration of the antenna that is often desired so that the antenna itself is aesthetic or conveys information, rather than standing out as a solely functional item.
According to the present invention the above mentioned problems are solved by applying a conductive foil or a film to a substrate in such a way that a high grade antenna for RFID transmission is provided yet can be produced quickly and inexpensively and in a manner which is aesthetic or conveys information. According to one aspect of the present invention, the process and equipment disclosed in U.S. Pat. No. 5,520,763 (the disclosure of which is hereby incorporated by reference herein) may be utilized to produce the antenna, or according to another aspect of the present invention an even more simplified construction may be provided.
According to one aspect of the present invention there is provided a radio frequency antenna-containing element comprising: A flexible substrate having a top surface. Adhesive in a radio frequency antenna configuration operatively connected to the top surface. A conductive foil or film operatively connected to the adhesive so as to have substantially the same configuration thereof, and on the opposite side of the adhesive from the top surface. And, the conductive foil or film having a radio frequency antenna configuration and the substrate with the adhesive and foil or film being flexible and bendable without destroying the substrate or antenna configuration of the foil or film.
The substrate preferably comprises paper, thin sheets of plastic, or like materials. For example a particularly desirable substrate is conventional card stock paper, although bond paper, or paper heavier than card stock, may also be utilized. Readily bendable polypropylene or polyolefin sheets having a thickness approximately that of bond paper also may be utilized. Preferably the substrate has the appropriate flexibility and bendability properties so that it may be readily handled in web form, and relatively high speed equipment, so that radio frequency antenna-containing elements according to the invention may be produced at web speeds of at least 50 feet per minute, and preferably over about 100 feet per minute.
The adhesive may comprise either permanent or removable hot melt pressure sensitive adhesive and in one preferred embodiment the adhesive is substantially directly adhered to the substrate and the conductive foil or film. The adhesive coat weight may be between about 3-6 pounds per 17 inch by 22 inch by 500 sheet ream of substrate (that is 3-6 pounds per surface area which is 17 inches by 22 inches times 500). The conductive foil or film may have a thickness of between about 0.3-1 mil and may have a wide variety of metallic colors. The adhesive and conductive foil or film configurations preferably have the configurations of letters or numbers so that they can convey information, or are otherwise in aesthetic patterns which do not allow an observer to easily discern that the foil or film is an RF antenna.
Alternatively, pursuant to the procedures in, and utilizing the equipment such as shown in, U.S. Pat. No. 5,520,763, toner may be printed onto the substrate, preferably when it is in the form of a web, so that the toner is disposed between the substrate top surface and the adhesive, the toner also having substantially the same configuration as the adhesive and conductive foil or film, such as described above.
According to another aspect of the present invention there is provided a method of making a radio frequency antenna-containing element comprising: (a) Applying a pressure sensitive adhesive substantially directly to the top surface of a flexible substrate so that the adhesive is in the form of a pattern of a radio frequency antenna. (b) Laminating a conductive foil or film to the adhesive on the top face of the substrate. And, (c) removing the conductive foil or film from the top face of the substrate except for where the conductive foil or film adheres to the adhesive, to produce a flexible substrate having a flexible radio frequency antenna adhered thereto.
In the implementation of the method described above preferably (b) and (c) are practiced by bringing a sheet or web of the conductive foil or film into secure contact with the adhesive, and then taking up the web or sheet so that the portions of the web or sheet not engaging the adhesive are torn away from those portions of the web or sheet that do engage the adhesive. Also preferably (a) is practiced by applying a hot melt adhesive at a coat weigh of between about 3-6 pounds per 17 inch by 22 inch by 500 sheet ream of substrate, and also preferably (b) is practiced utilizing a conductive foil or film having a thickness of about 0.3-1 mil. In one preferred embodiment (a)-(c) are practiced so as to apply the adhesive and conductive foil or film so that they have the configurations of letters or numbers; or so that the conductive foil or film otherwise is not readily discernible as a functioning RF antenna.
The method of the invention may also include providing other RF circuit elements, such as an RF chip, in operative association with the antenna, such as is conventional or as shown in U.S. application Ser. No. 09/393,291 filed Sep. 10, 1999, and if it is desired that the element produced be a label or the like, pressure sensitive adhesive can be applied to the bottom surface of the substrate and may be covered by a release liner.
Also in the practice of the method (b) may be practiced to unwind a web of conductive foil or film to bring the web of conductive foil or film into contact with the adhesive, and (c) may be practiced to rewind the web of conductive foil or film so that the portions of the web not engaging the adhesive are torn away from those portions of the web that do engage the adhesive.
According to another aspect of the present invention, utilizing the basic procedures and equipment as disclosed in U.S. Pat. No. 5,520,763, there is provided a method of making a radio frequency antenna-containing element comprising: (a) Printing a toner on the top surface of a flexible substrate so that the toner is in the form of a pattern of a radio frequency antenna. (b) Heating the toner to make it tacky. (c) While the toner is tacky, applying a laminate of a conductive foil or film and adhesive onto the toner while heating and applying pressure, so that the adhesive and foil stick to the toner where they engage. And, (d) removing the laminate from the substrate except for where the conductive foil or film and adhesive adhere to the toner, to produce a flexible substrate having a flexible radio frequency antenna operatively adhered thereto.
In this aspect of the invention preferably (a)-(d) are preferably practiced so as to apply the adhesive and conductive foil or film so that they have the configurations of letters or numbers. Also preferably according to this aspect (c) is practiced to unwind a web of a laminate of adhesive and conductive foil or film to bring the web into contact with the tacky toner, and (d) is practiced to rewind the laminate web so that the portions of the web not engaging the toner are torn away from those portions of the web that do engage the toner.
It is the primary object of the present invention to be able to easily and quickly produce an element having a high grade antenna for RFID transmissions. This and other aspects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.